1. Field of the Invention
This invention relates to flame retardant polyester resin compositions reinforced with glass fiber having outstanding mechanical and thermal properties as well as good forming and machining propeties.
2. Description of the Prior Art
Glass fiber reinforced products produced with polyester resin, such as polyethylene terephthalate and polybutylene terephthalate resins, have been used in numerous applications as a type of engineering plastic. Such reinforced resins are known for their outstanding physical properties, for example for their mechanical, thermal, and chemical resistance and for their forming and machining properties. On the other hand the glass fiber reinforced polyester resin has the distinct disadvantage of flammability, as do other synthetic resins. Accordingly flame retardancy is an important property for engineering plastics.
Normally untreated polyethylene terephthalate or polybutylene terephthalate resin products reinforced with glass fibers require a comparatively high molding temperature, for example in the range of about 240.degree. to 300.degree. C. This means that in order to be considered for incorporation into a polyester resin/glass fiber composition, a candidate flame retardant must itself exhibit good heat resistivity. This means one must use flame retardants that will only be degraded, if at all, at the high molding temperatures. Further, they must not impart color to nor deteriorate the resin properties in the ultimately molded products. Since polyethylene terephthalate resin/glass fiber reinforced products themselves have a high heat distortion temperature, they are typically used in comprehensive applications exposed to high temperatures, for example in electric appliances and the like. Consequently, the successful flame retardation of polyester resin/glass fiber reinforced products, as mentioned above, requires the molded articles to be thermally stable. That is, they should be free from deterioration in their flame retardant properties due to heat dissipation if the finished products are exposed to high temperatures over long term operations while still providing the required basic properties which include flame retardance, mechanical strength, heat resistance and the like.
Considering the above performance requirements, commonly assigned to U.S. Pat. No. 3,965,212, issued on June 22, 1976 describes flame retardant resin compositions which contain the flame retardant represented by general formula (I), described below, together with antimony trioxide in a particular relationship, combined together in a glass fiber reinforced polyethylene terephthalate resin composition. However, further investigations have revealed that the above-mentioned resin compositions may suffer from a deterioration in forming properties depending upon the molding conditions used. As examples this may occur in the case of increased temperature in the course of the extrusion or injection process, or a prolonged residence time in the mold. This is particularly true in the system where a flame retardant represented by the general formula (I) is much contained; fluidity deterioration is substantial. As a result restrictions are imposed on the molding machine type, molding conditions, injection volume, etc.
Glass fiber reinforced polybutylene terephthalate resin to which has been added the same flame retardant and antimony trioxide in general provides outstanding flame retardancy, acceptable mechanical properties, forming and machining properties and the like. However, in a system where the flame retardant represented by the general formula (I) is much contained a considerable drop in the heat distortion temperature occurs, causing the problem of heat resistance. It is to this problem that the present invention is directed.